The present invention relates to an anti-lock hydraulic brake system which includes a master brake cylinder, a pump, an inlet valve and an outlet valve. The inlet valve is a minimum element whose control compartments are connected through a throttle.
A brake system of this type is known from U.S. Pat. No. 4,715,666. The pressure-fluid collecting means of this system is integrated in the housing of the pump and is confined by a piston which is supported on the pump piston by way of a spring. After the outlet valve is opened, the chamber is filled with pressure fluid, whereby the piston confining the chamber displaces and presses the pump piston against an eccentric. This eccentric drives the pump piston, with the bias of the spring changing as a result and thus the pressure in the pressure-fluid collecting means. This pressure simultaneously is the inlet pressure for the pump. However, since the inlet pressure also determines the delivery rate of the pump, the latter varies as well.
In order to generate an approximately even pressure fluid flow in the control phase, it is necessary to provide the throttle which connects the return line to the brake line as a flow control valve. The flow control rate in a flow control valve is independent of the pressure gradient at the flow control valve. A valve of this type is composed of a throttle with constant cross-section and a throttle with variable cross-section. The varying cross-section is caused by a displaceable piston which in an opposite sense is loaded by the pressures in front of and behind the throttle with constant cross-section. Such a flow control valve has a considerably more complicated structure than a throttle with constant cross-section, which, for example, is formed by a line constriction. Therefore, it is an object of the present invention to provide such brake system with less structural effort and to achieve an even flow of pressure fluid from the pump to the wheel brake nonetheless.